High-contrast liquid crystal displays utilizing advantages of the birefringent properties of liquid crystals of the STN type and other types are being used as the displays of personal computers, word processors, and others. Such liquid crystal displays have a problem that since incident light is converted to linearly polarized light by the polarizing plate and then to elliptically polarized light due to the birefringence of the liquid crystal cell, the display assumes a yellow to blue color when the elliptically polarized light is viewed through the polarizing plate. As an expedient for reconverting elliptically polarized light which has passed through a liquid crystal cell to linearly polarized light by compensating the phase difference caused by the birefringence of the liquid crystal cell thereby to eliminate the above-described coloring problem, an FTN-type display has been proposed in which a retardation film comprising an oriented film is provided between a liquid crystal cell and a polarizing plate.
Use of an ordinary oriented film as the retardation film in the above FTN-type display, however, has proved to be defective in visibility and recognizability because the viewing angle range in which the display can be viewed as a black-and-white display is narrow since the display assumes a yellow to blue color if the viewing point shifts only little and because the viewing angle range in which the display can be viewed with good contrast is also narrow. Retardation films which have controlled refractive indexes in the thickness direction and can attain widened viewing angle ranges have been proposed in JP-A-2-47629 and JP-A-2-160204. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, the retardation film proposed in JP-A-2-47629, which is obtained by monoaxially stretching a film made of a resin showing negative birefringence, i.e., having a reduced refractive index in the stretch direction, has a problem that because of the limited kinds of such resins showing negative birefringence, the range of the selection of refractive indexes for controlling reflection loss caused at the interface between the retardation film and a glass plate or the like is considerably limited, and also has another problem that a sufficiently large difference in refractive index between respective directions cannot be attained by the stretching treatment.
On the other hand, the retardation film proposed in JP-A-2-160204, which is obtained by slicing an extruded rod and stretching the sliced plate in which the molecules are oriented in the thickness direction, has been defective in that the production efficiency therefor is low. This technique further has a problem that it is difficult to obtain a large-sized retardation film applicable, for example, to large liquid crystal displays for high definition television, etc.